In recent years, biodegradable resins typified by polylactic acid have come into focus from the viewpoint of environmental preservation. The polylactic acid is one of the most heat-resistant and highly transparent biodegradable resins, and is mass-producible from a material derived from plants such as corn and sweet potato. Therefore, the polylactic acid is less expensive. In addition, the polylactic acid is contributable to reduction in oil consumption and hence is very useful. However, the biodegradable resin is still unsatisfactory for use as a material for containers and packages which are required to have gas and liquid barrier properties.
An exemplary method for improving the gas barrier property of the biodegradable resin is to add a phyllosilicate organically treated with a specific ammonium ion to the biodegradable resin as disclosed in JP-A-2002-338796. This document states that the addition improves the strength and the gas barrier property of the resin. Further, a method of coating a biodegradable plastic with a metal oxide such as silicon oxide by a chemical vapor phase method is disclosed in JP-A-2002-068201. These methods ensure an excellent gas barrier property, but are unsatisfactory in environmental consideration and attribution to the plant-based material.